EFFECTS OF DIFFERENT SHADED CONDITIONS AND WATER DEPTHS ON THE GROWTH AND REPRODUCTIVE STRATEGY OF VALLISNERIA SPINULOSA

Abstract

The occurrence and growth of submerged macrophytes mainly depends on a suitable light environment. Nowadays, however, lake eutrophication increasing phytoplankton and epiphyton overgrowth has caused shading habitats. This change influences light quantity and quality under lake water. The decrease of light availability will play a spectacular and unusual role on the establishment, growth and survival of submerged macrophytes. So the effects of four shaded treatments and three water depth treatments on the growth and reproductive strategy of Vallisneria Spinulosa were carried out to investingate how light availability imposed an adverse influences on the growth and reproduction of submerged macrophytes. This study confirmed that both light quality and quantity affected by shaded treatments and water depth treatments had negative impacts on growth, reproduction and the associated morphological traits of V. spinulosa. Compared to shaded treatments,the effect of water-depth gradient on sexual reproduction was less significantly different. The treatments of sunshades associated light attenuation played a determinant role in the growth and reproductive strategy of macrophyte V. spinulosa, while the depth gradients had a scaling effect. In addition, length of the total stolons, number of inflorescences, stolon biomass, seed biomass, total biomass, and resource allocation ratios of seeds and ratios between above-ground biomass and below-ground biomass per plant were relatively insensitive to light quantity and quality affected by water depth treatments. Resource allocation ratios of tubers was less changeable to light quantity and quality affected by shaded treatments. So the effects of irradiance decrease has been suggested to be the main reason for the disappearance of submerged macrophytes from eutrophic waters owing to shaded effects.